More assertions.

src/display/bitmapfont.c

@@ -11,6 +11,9 @@ tilesetdiv_t * bitmapFontGetCharacterDivision(tileset_t *tileset,
   char character
 ) {
   int32_t i = ((int32_t)character) - BITMAP_FONT_CHAR_START;
+
+  ASSERT_NOT_NULL(tileset);
+
   return tileset->divisions + i;
 }
 
@@ -24,6 +27,10 @@ bitmapfontmeasure_t bitmapFontMeasure(char *string,
     .height = 0, .lines = 1, .width = 0
   };
 
+  ASSERT_NOT_NULL(string);
+  ASSERT_GREATER_THAN(charWidth, 0);
+  ASSERT_GREATER_THAN(charHeight, 0);
+
   i = 0;
   y = 0;
   x = 0;